Leo Tolstoy famously opens his novel Anna Karenina with the words, "All happy families are alike; each unhappy family is unhappy in its own way." Statisticians have derived from here something they've come to call the "Anna Karenina principle"—roughly, the idea that success in any enterprise requires that everything go right: remove a single important prerequisite, and your endeavor will fail.  Say the preconditions of success are A, B, C, and D.
Then in every successful case, all of A, B, C, and D, will be in place, but each failure may have its own profile. Lack of success may be due to the absence of A, or B, or C and D, and so on.Read more on psychologytoday.com